Canonical said in a security advisory dated 28 October 2026 that a critical vulnerability affecting LXD and MicroCloud, referred to it by the Incus project, allows an attacker able to reach the LXD HTTPS API to authenticate as any trusted TLS client for which the attacker has the public certificate.

Canonical says the mutual TLS authentication logic compared all certificates sent by the client against the trust store, although only the leaf certificate proves ownership of the signing key, so an attacker could place a trusted client's public certificate as an intermediate certificate in the chain.

In MicroCloud, Canonical says an attacker can intercept the public TLS certificate of a joining cluster member and then authenticate as that member, and that depending on the privilege of the impersonated user the attacker may gain root access to the host machine.

Canonical urges all LXD and MicroCloud users to update immediately and says the LXD point releases are in progressive roll-out from candidate to stable. (source: Canonical)

The CVE record, published by Canonical as CNA, lists affected LXD versions 4.0.14, 5.0.10, 5.21.8 and 6.9 before 4.0.15, 5.0.11, 5.21.9 and 6.10.1, rates the flaw CVSS 4.0 10.0 (Critical), and carries a CISA assessment dated 30 October 2026 of exploitation: none. (source: CVE record)